It is known that, in preparation for final assembly of sheet metal plates, for example by riveting, said metal plates are generally temporarily assembled by means of pinning clips passing through holes in register made therein.
Such plate pinning clips are for example described in French Patent No. FR-A-789945 of May 13, 1935, in its Certificate of Addition FR-A-48048 of May 13, 1936, or in French Patent No. FR-A-1 492 310 of July 8, 1966.
Known pinning clips comprise a bearing face adapted to come into contact with the outer face of an outer plate of the assembly of sheet metal plates, at least one elongated element provided with a hooking beak and adapted to move parallel to said plates so that said beak is capable of hooking behind the outer face of the other outer plate of said assembly of sheet metal plates, on the edge of the corresponding hole, and means for creating a relative displacement between said bearing face and said hooking beak, so that said plates are pressed between the latter.
Furthermore, it is known that more or less viscous and generally polymerizable products, serving to provide protection against corrosion and/or a seal, or for any other reason, are being interposed more and more between the different sheet metal plates.
Such products of interposition must be locally eliminated by creeping, before polymerization, at the points of fixation, in order to allow correct assembly, as is explained, for example, in French Patent No. FR-A-1 492 310.
Under these conditions, the pinning clips must apply a considerable effort to bring the plates together up to metal-metal contact; the interposed products creep and are partially distributed in the holes in which the clips are disposed and polymerize there. Consequently, said clips are soiled by the interposed product, are difficult to withdraw when it is desired to install the final fastening means (this frequently causing deformations or breaks of the clips), and must be cleaned before being used again, with the result that the life duration of these clips is very short. For clips of large diameter in particular, for which the efforts to be applied are considerable, the creep and polymerization of the interposed products cause a deterioration of the clips, such that the latter can hardly be used more than once. Since these clips are relatively expensive, it is preferred to replace them by bolts, this generally requiring the presence of two persons, one on the screw side, the other on the nut side (bolts which, moreover, must be tightened as the product creeps).